An image forming apparatus is capable of forming an image on print media, such as, for example, sheets of paper. Examples of an image forming apparatus may include a printer, a copier, a fax machine and a multi-function peripheral that combine at least two functions of aforementioned.
Some image forming apparatuses include a bookbinding unit that receives from the image forming apparatus print media on which a complete image has been formed, and that binds together the received print media.
To that end, a bookbinding unit typically includes a pair of stack trays arranged side by side with a space gap between them. The received print media are stacked on the stack trays, and become folded when a folding knife presses and pushes the stacked print media through the space between the stack trays.
In such a bookbinding unit, a considerable portion of the pressing force exerted on the print media by the folding knife is concentrated near the space between the two stack trays, and as the folded print media are pushed through the space between the stack trays, the outermost print medium may be subjected to a significant frictional force by the edges of the two stack trays, and thus may become damaged.